Coming in at number 15, St. Jimmy is the drug-addict friend/alter-ego of Jesus of Suburbia in the American Idiot story. Billie Joe has also said in the past that the character represents part of himself as well.

From NME:

"'King of the forty thieves I'm here to represent / That needle in the vein of the establishment,' rasps Billie Joe Armstrong in this track from 'American Idiot'."

Other characters in the list include "Iron Man," "Major Tom," and "Billie Jean," amongst others. The full list can be viewed here.